This invention is directed to a method of fabricating a display with semiconductor integrated circuits combined therewith on the same substrate as a monolithic display structure and a flat panel display as so formed thereby. More specifically, the invention concerns a method of fabricating a display, which may be of the liquid crystal or electrochromic type, for example, as an x-y matrix display with a corresponding array of silicon address transistors in the form of metal-oxide-semiconductor field effect transistors (MOSFETS) on a monolithic structure and the flat panel display produced thereby, wherein polysilicon material as disposed on a substrate such as transparent quartz or a glass plate is subjected to a laser annealing treatment to enable the formation of silicon integrated circuits in the resulting crystalline silicon including the address transistors for the matrix display by enhancing the electron mobility characteristic of the laser-annealed polysilicon material.
Basically, a visual electronic display requires appropriate electrical stimulation at various positions in the plane where the information to be displayed is being written. Conversion of the electrical stimulation into an optical signal by an electrooptic element, such as a liquid crystal material in concert with respective electrodes, or an electrochromic or electroluminescent element, is then necessary to provide the visual display. Large information content displays require a structure in which a spatially inhomogeneous distribution of charge independent of the number of elements in the total display is accomplished. Heretofore, x-y matrix addressing has been effective for low and intermediate information content displays, but falters when the display is expanded in size to be one of large information content (i.e., where the number N of lines driven is greater than 100). In this connection, direct matrix addressing of N lines only presents the display data to a given line 1/N of the refresh time--typically 30 nsec. As N increases, either the display element will not give sufficient light or the contrast of the display decreases to such an extent that the display becomes unusable. In order to obtain high brightness and/or high contrast for large magnitude of N, the electronic signal to a given display cell unit or pixel must be made independent of N. This is accomplished by providing a switch for each pixel so that the pixel is connected for a substantial portion of the refresh time to its own dedicated source of data. N.sup.2 switches are required to do this which involves a switch-distribution problem.
Such electronic x-y matrix displays have been the subject of intensive efforts to develop a reliable structure capable of handling a large information content. One such proposal involves the use of deposited thin film transistors (TFT's) on glass, wherein the transistors are fabricated from CdS or CdSe. This type of display suffers from low reliability in terms of number of total cycle times before breakdown and generally has an unsatisfactory relatively short lifetime.
Another approach to the x-y matrix display has involved the fabrication of switching transistors on a monocrystalline silicon substrate. This approach necessitates the fabrication of monocrystalline silicon over the large display area which is required for human interaction resulting in significant costs, and further suffering from the drawback that the monocrystalline silicon substrate is opaque to light.
Thus, efforts to develop reliable display structures in which the peripheral circuitry including circuitry to drive the respective display electrode elements is disposed on the same substrate as the display elements have generally been unavailing heretofore for a variety of reasons. One such instance of a display device combined with peripheral electronics for driving the display in a monolithic structure is disclosed in U.S. Pat. No. 3,765,747 Pankratz et al issued Oct. 16, 1973, wherein a liquid crystal display is combined with driver circuitry on the same substrate. The liquid crystal display is described as being either of the seven segment type as used for displaying numbers between 0 and 9 or as a dot display in which the pattern to be displayed is formed on a series of dots arranged in an x-y matrix. In liquid crystal displays using matrix addressing to generate a dot-type display, the character to be displayed is defined by a series of dots which are placed at positions conforming to the outline of the desired pattern. In the aforesaid U.S. Pat. No. 3,765,747, the liquid crystal display of dot-type is defined on a substrate of silicon material of one conductivity type wherein a plurality of diodes are formed on the substrate, such that each diode is respectively disposed in series with a corresponding one of the display elements to enable the addressing of the matrix in the so-called scan mode. In this connection, first and second sets of electrodes which are orthogonally oriented with respect to each other are provided on the substrate, with one first set of electrodes being formed in one surface of the substrate as a series of thin parallel conductors, and the second set of electrodes being formed as conductive strips in a patterned conductive layer applied as a coating to the top transparent electrode of the display. The intersection points of respective electrodes of the two sets define a matrix of points or dots corresponding to the respective diodes and the display elements connected in series therewith. By applying voltages to selected elements of each of the two sets of orthogonally related electrodes, the crossing points of those electrodes which are energized bias the liquid crystal composition therebetween to cause light modulation in a manner displaying a dot. By selectively energizing the first and second sets of orthogonally related electrodes, the liquid crystal composition can be addressed in the so-called x-y scan mode with each of the display elements having an isolated and individual diode in series therewith to define a dot matrix liquid crystal display.
The aforesaid liquid crystal display of an x-y matrix dot type as disclosed in U.S. Pat. No. 3,765,747 has a light-opaque monocrystalline silicon substrate in the manner of the previously discussed approach wherein switching transistors are proposed in conjunction with the individual display cell units or pixels rather than diodes, although a description of a transparent mode liquid crystal display device occurs therein on the assumption that a silicon substrate may be thinned sufficiently to be light-transmissive.